Although candles have been produced for millennia, certain problems in candle production still remain. Specifically, candle producers desire candle waxes that demonstrate little or no shrinkage, little or no oil bleed, a pleasing and stable appearance and the ability to retain fragrance. Candles are traditionally made of petroleum derived waxes with mostly normal paraffin (n-paraffin) content, lower molecular weights, and therefore lower melting points. While candles with high n-paraffin content retain the proper color and texture desired by candle makers, they are often plagued by excessive shrinkage and poor fragrance retention.
While all of the above properties are important to candle makers, the most important property is the melting point of the wax. Candle makers use Fully Refined Waxes (“FRW”), which usually have less than 1% oil content, as the largest, if not only, wax type in their candles. On occasion, candle makers add microwax or polymers, to enhance the candle's properties, but these additives are costly relative to the wax. Low Melting (“LM”) point wax usually melts at 128° F. (53° C.) or less. Waxes of this type are typically used for container candles, i.e., religious novena candles and decorative, fragranced jar candles. Typically LM FRW is gray in appearance and demonstrate relatively high shrinkage. Mid Melting (“MM”) point waxes usually melt between 128 and 145° F. (53-63° C.) and are often used for higher quality container candles and free standing candles. MM RHC™ FRW are gray in appearance and demonstrate only slightly less shrinkage than LM FRW.
High Melting (“HM”) point waxes, melting at greater than 145° F. (63° C.), are not commonly used in the candle industry. While waxes of this type typically demonstrate less shrinkage than either LM or MM RHC™ waxes, other significant disadvantages have prevented their use in the candle industry. HM FRW waxes are not used as candles because they exhibit a “tunneling” effect. That is, the candle burns straight down into the candle, leaving walled sides. The tunneling effect has proven highly commercially unattractive for both jar and stand-alone candles. The tunneling effect is caused because the “pool” of liquid wax that forms on the top surface of a burning candle does not extend far from the flame, due to the high melting point of the wax. Thus, the candle tends to be consumed unevenly, carving out a cylinder in the center of the candle. A solution to this problem would be to use a larger wick, but this produces a larger and higher flame—again a commercially unattractive option.
Shrinkage is a common problem experienced in candle manufacture. As a molten candle wax solidifies, the volume shrinks. In some cases this shrinkage can be beneficial, for example in helping a poured candle pull away from the sides of a mold making it easier to remove. However, wax shrinkage usually produces an unwanted concave effect on the top of the candle. Candle manufacturers must often re-melt the top portion of the candle or even resort to a second pouring of the candle wax formulation to level the top should excess shrinkage occur. In container candles, shrinkage can lead to candle separation from the side of the container—another undesired effect. Shrinkage has been directly linked to the amount of n-paraffin in the candle wax. Candle waxes containing about 100% n-paraffin will shrink approximately 12 to 15% by volume on cooling. Candle waxes containing about 75% n-paraffin will shrink approximately 8 to 12% by volume on cooling. Candle waxes containing about 50% n-paraffin will shrink approximately 6 to 8% by volume on cooling.
Several methods have been developed in an effort to control excessive shrinkage in container candles. Typically shrinkage is controlled by introducing components that will disrupt the n-paraffin crystal formation. Historically, the addition of high molecular weight isoparaffins (in the form of microwax or petrolatum), oxygenated molecules (such as carboxylic acids, carboxylate esters) and polyol structures have helped control shrinkage. However, these solutions are usually costly, can alter the color and texture of the candle, and, in some cases, raise the melting point to an unacceptably high level.
Another significant concern for candle makers is oil bleed. Oil bleed can be defined as the migration of oil or oil-type molecules out of and onto the surface of the solid wax. The appearance of oil on the wax candle surface is generally regarded as an unacceptable appearance phenomenon. The oil can be derived from the natural oil content of the petroleum wax or from added oily components in the candle formulation, including fragrance oils and carrier solvents for fragrance packages. Petroleum waxes of all types contain some amount of oil. Fully refined waxes have typically less than 1%, more often less -than 0.5%, oil content (as measured by the ASTM D-721 test method). Scale waxes are low oil content slack waxes. With further refinement to improve color and odor, typically by hydrotreatment, scale waxes can be upgraded to semi-refined waxes that can have from 1% to about 5% oil content (as measured by the ASTM D-721 test method). Semi-refined waxes have found limited use in container candles, in spite of their typically lower cost, because of a greater tendency to exhibit oil bleed in a formulated candle.
Historically, methods for improving oil bleed or fragrance hold in candle manufacture include:    1. addition of high molecular weight microwax (derived from bright stock),    2. addition of petrolatum (petroleum jelly),    3. addition of other additives, and    4. rigorous control of process conditions, such as cooling rates and sequences.
While helping to minimize oil bleed, the addition of microwax and modified waxes often causes additional problems of shrinkage (see above). The addition of petrolatum or petroleum jelly is relatively expensive and significantly softens the candle. Other additives can also be expensive and/or can negatively alter the appearance and shrinkage characteristics of the wax and candle formulation. Finally, varying the cooling rates and sequences is labor intensive and often varies with the slightest difference in the underlying candle wax.
Another important attribute for candle manufacturers is the color and uniformity of the raw candle. The impact of raw wax color and appearance on the final candle formulation can be significant. For example, a translucent gray LM fully refined wax will provide a different appearance in a given candle formulation than higher melting, more isoparaffinic wax that has a more cloudy, white-gray appearance. Candle makers typically formulate for a given type of base wax and strive to maintain a consistent color and appearance for each candle formulation. A wax that exhibits a rich, creamy opaque whiteness can provide the candle maker with new and improved options for candle formulation.